[albatros]

I have now documented the individual steps:

1: create a new setlist ("testlist") and add 2 songs ("song1" and "song2")
2: "testlist" has 2 songs (green marking)
3: both songs are displayed
4: during the display of "song1" select "edit"
5+6: remove the setlists-entry
7: after save "song2" is displayed (correct, because "song1" is no longer in the list)
8: back to the library - the list is still displayed with 2 songs (red marking)
9: after selecting the list again only song2 is displayed and the correct number of songs is shown in the title bar

the error can be seen in picture 8

by the way: 
it is a bit confusing that the number in brackets after "setlists" shows the number of lists (picture 2) and then the number of songs 
in the selected list (picture 3), especially since in the second case "setlists" is in the plural although 1 list is selected (yellow marking)